Theresa May will argue that abuse is disproportionately aimed at female, BAME and LGBT people.
Photograph: Jonathan Brady/PA

Theresa May will mark the centenary of the 1918 Representation of the People Act on Tuesday by warning that abuse in public life has become so severe it is threatening democracy.

The prime minister will give a speech in Manchester marking the anniversary of the act, which extended the parliamentary vote to some women and paved the way for universal suffrage 10 years later.

As well as celebrating the achievements of the suffragettes, she will warn that the tone of political life is deteriorating – and set out a series of steps the government will take to crack down on abuse.

“While there is much to celebrate, I worry that our public debate today is coarsening. That for some it is becoming harder to disagree, without also demeaning opposing viewpoints in the process.

“In the face of what is a threat to our democracy, I believe that all of us – individuals, governments, and media old and new – must accept our responsibility to help sustain a genuinely pluralist public debate for the future,” she will say.

“It is online where some of the most troubling behaviour now occurs … As well as being places for empowering self-expression, online platforms can become places of intimidation and abuse … This squanders the opportunity new technology affords us to drive up political engagement, and can have the perverse effect of putting off participation from those who are not prepared to tolerate the levels of abuse which exist.”

She will argue that abuse is disproportionately targeted at female, BME and LGBT people.

Research conducted by Amnesty International last year found that the shadow home secretary, Diane Abbott, had received almost half the abusive tweets sent to female MPs in the run-up to the general election.

The committee called for Twitter, Facebook and Google to report quarterly on how many reports of abuse they receive, the percentage of reported content that is taken down, and the time it takes them to do so.

What can be done about abuse on social media?

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The government will also publish a new social media code of practice, setting out firms’ obligations.

May will also announce that the government will ask the Law Commission to review legislation covering “offensive online communications”, “to ensure that the criminal law, which was drafted long before the creation of social media platforms, is appropriate to meet the challenges posed by this new technology”.

Other recommendations from the committee on standards in public life that May is expected to endorse include a specific offence of intimidating a political candidate.

The report said: “Government should consult on the introduction of a new offence in electoral law of intimidating parliamentary candidates and party campaigners.”

Jeremy Corbyn’s shadow cabinet will tour an exhibition on the suffragettes at the Museum of London to mark the anniversary on Tuesday.

Dawn Butler, shadow minister for women and equalities, said: “This centenary is an important landmark for women – it highlights the importance of inclusion and equality. It opened doors for some women to vote and be elected to parliament. But it wasn’t totally inclusive. It illustrates that every battle is worth the fight, as it takes us a step closer to equality, but we must never stop fighting.”